Because LCD devices have the advantages of portability, low power consumption, and low radiation, they have been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras, and the like. Furthermore, LCD devices are considered by many to have the potential to completely replace cathode ray tube (CRT) monitors and televisions.
A conventional LCD device includes a pair of transparent substrates a transparent electrode and an alignment film provided on an inner surface of each of the transparent substrates, an LC layer sandwiched between the two alignment films, a polarizer arranged at an outside surface of each transparent substrate. Polarization directions of the two polarizers are perpendicular to each other. LC molecules of the liquid crystal layer between the transparent substrates are twisted at angles of 90° or 135°. This kind of LCD device is called a twisted nematic (TN) type LCD device or a super-twisted nematic (STN) type LCD device.
When no voltage is applied between the two transparent electrodes, the LC molecules of the LC layer maintain orientations parallel to the transparent substrates. A polarization of polarized light beams entering the liquid crystal layer is rotated along with the LC molecules, and the light beams can transmit out of the LCD device. The LCD device is thus in an on-state. When an appropriate voltage is applied between the two transparent electrodes, the LC molecules are oriented with long axes thereof being perpendicular to the two transparent substrates. Then light beams entering the liquid crystal layer cannot pass through, and so do not transmit out of the LCD device. The LCD device is thus in an off-state.
A so-called anchoring energy exists between the LC molecules and the adjacent alignment films. Due to the anchoring energy, when the LCD device is in an off-state, LC molecules adjacent to the alignment films cannot be oriented completely perpendicular to the transparent substrates. Thus, part of the incoming light beams leaks out of the LCD device. Accordingly, the LCD device cannot display a completely black picture. This also means the LCD device has a low contrast ratio and a narrow viewing angle.
Accordingly, what is needed is an LCD device that can overcome the above-described deficiencies.